OPN+OPLL MegaMod - YM2203 & YM2413 Combo

What is it?

The OPN+OPLL MegaMod is a dual-chip music module combining the YM2203 (OPN) and YM2413 (OPLL) on a single MegaGRRL-compatible board. Plug it into your MegaGRRL and unlock authentic playback of MSX-Music and PC-88/PC-98 VGM/VGZ format music — all from real hardware chips, not emulation.

Why Was It Made?

In 2023, the desire to play MSX-Music through MegaGRRL led to a collaboration between Denjhang (PCB design) and Natalie (firmware/programming). After 5 iterative versions, the OPN+OPLL MegaMod was born — a refined, feature-complete module that handles the unique challenges of mixing OPN and OPLL audio with independent volume control and clean output.

What Makes It Special?

• YM2413 differential amplifier circuit with single 5V power supply — pure sound quality and high volume output
• Independent volume potentiometers for OPLL, OPN, and SSG — fine-tune each sound source separately
• Total master volume potentiometer for overall level control
• SSG stereo switch — freely configure stereo or mono SSG output
• Chip select signal indicator LEDs — simple visual feedback showing which chip is active
• 5 versions of iterative development for refined, reliable performance

Supported Music Systems

• MSX-Music (OPLL): YM2413-based MSX music, FMPAC titles
• PC-88 / PC-98 (OPN): YM2203-based Japanese PC music
• SSG (PSG): Built-in 3-channel square wave from YM2203
• Format: VGM / VGZ

Key Specifications

• Chips: YM2203 (OPN) + YM2413 (OPLL)
• OPN: 3-channel FM + 3-channel SSG
• OPLL: 9-channel FM (or 6 FM + 5 rhythm)
• Volume control: Independent OPLL / OPN / SSG + master
• SSG output: Stereo switch on-board
• Power: Single 5V supply
• Module format: Standard MegaGRRL compatible
• Indicator: Chip select signal LEDs

Compatible Systems

• MegaGRRL Desktop (hardware VGM player)
• Any MegaGRRL-compatible host